Hi, On 2022-12-27 11:24:49 -0800, Nathan Bossart wrote: > I've attached a patch set that adds the restore_library, > archive_cleanup_library, and recovery_end_library parameters to allow > archive recovery via loadable modules. This is a follow-up to the > archive_library parameter added in v15 [0] [1].
Why do we need N parameters for this? To me it seems more sensible to have one parameter that then allows a library to implement all these (potentially optionally). > * Unlike archive modules, recovery libraries cannot be changed at runtime. > There isn't a safe way to unload a library, and archive libraries work > around this restriction by restarting the archiver process. Since recovery > libraries are loaded via the startup and checkpointer processes (which > cannot be trivially restarted like the archiver), the same workaround is > not feasible. I don't think that's a convincing reason to not support configuration changes. Sure, libraries cannot be unloaded, but an unnecessarily loaded library is cheap. All that's needed is to redirect the relevant function calls. > * pg_rewind uses restore_command, but there isn't a straightforward path to > support restore_library. I haven't addressed this in the attached patches, > but perhaps this is a reason to allow specifying both restore_command and > restore_library at the same time. pg_rewind would use restore_command, and > the server would use restore_library. That seems problematic, leading to situations where one might not be able to use restore_command anymore, because it's not feasible to do segment-by-segment restoration. Greetings, Andres Freund
